1. Field of the Invention
The present invention relates, in general, to metallurgical vessels and, more specifically, to top ring or lip closure devices for metallurgical vessels, such as ladles used in the steel industry.
2. State of the Art
Metallurgical vessels, such as ladles used in the steel industry for handling molten steel, are formed of an outer steel shell and a refractory brick inner lining. The refractory bricks are stacked along the bottom surface and the inner surface of the steel shell along the entire height of the ladle from the bottom to the top, open mouth of the ladle.
Refractory bricks transfer a thermal load, i.e., heat radiation from the molten steel, from a "hot face" immediately adjacent the molten steel to a "cold face", i.e., the refractory plane most distant from the molten metal and located adjacent to the outer steel shell. During steelmaking, the ladle is frequently tipped for steel pouring or slag skimming operations and completely upended for deslagging. In order to provide mechanical support for the refractory brick stack, it is known to form an inwardly extending, angled flange immediately adjacent the top end of the steel shell. A removable lip ring or lip closure ring is inserted inside of the flange and on top of the refractory brick stack. The lip closure ring is typically formed of a number of identical, arcuate segments cast from a refractory or ceramic material. A smaller segment or "key" is custom shaped and inserted between two adjacent segments to close the lip ring and to provide integrity in the ring to support the refractory brick stack.
Some types of lip rings or lip closures use bolts to secure the lip ring segments to the outer steel shell. However, the bolts tend to break under mechanical forces generated by irreversible expansion and are not as favored as the angled closure flange and lip closure ring described above.
All such metallurgical vessels have a maximum service life limit before the refractory bricks must be replaced. Such a limit, which can be from twenty to twenty-five heats of molten steel, is determined in part by the life of the refractory bricks which are continually consumed by the repeated thermal transfer cycles of heat from the molten steel to the outer shell. Further, the service life limit is effected by the expansion of the refractory bricks from their original cold-cure state during initial burn in and the first few heats. Most of the expansion, which can be as much as 21/2 inches over the entire height of the refractory brick stack, occurs during the first few heats and remains constant thereafter for the service life of the brick stack. This expansion exerts a considerable force on the lip closure ring which can cause deformation, warpage or even breakage of the ring and thereby reduce or limit the useful service life of the vessel.
Thus, it would be desirable to provide a lip closure ring apparatus which overcomes the problems encountered with previously constructed lip closure rings. It would also be desirable to provide a lip closure ring apparatus which resists deformation despite thermal expansion of a refractory brick stack. It would also be desirable to provide a lip closure ring apparatus which increases the useful service life of a metallurgical vessel.